1. Field of the Invention
This invention relates to control devices for air conditioners, and more particularly to control devices for air conditioners which are capable of creating an optimum temperature environment under various conditions.
2. Description of the Prior Art
There are a variety of air conditioning systems; most widely used among them are self-contained small units which are utilized for conditioning a single room, etc. These small self-contained air conditioners usually comprise a compressor for circulating a refrigerant gas in a heat pump system, and are installed in a room to deliver warmed or cooled air thereto. Since the warmed or cooled air is sent out from an indoor unit of a small dimension in the case of such air conditioners, there tends to develop an unevenness in the distribution of temperature in the room. Thus, although these air conditioners comprise a room temperature sensor and the operation of the compressor is controlled in such a way that the detected room temperature may approach a target temperature, it often happens that the temperature environment in the room is deviated from the optimum condition.
FIGS. 1 and 2 show a conventional air conditioner disclosed, for example, in the Japanese patent publication No. 60-1253. An alternating current power supplied from the power source 1 is rectified by a rectifier circuit 2, and the direct current power outputted from the rectifier circuit 2 is supplied to an inverter 3, which outputs an alternating current power of variable frequency. The inverter 3 is capable of varying the output frequency continuously in the range of about from 25 to 80 Hz., thereby changing the rotational speed of the compressor 4 of the air conditioner in the range of from 1400 to 4500 rpm. The output frequency of the inverter 3 is controlled by a digital control signal outputted from the control device 5 which comprises a microcomputer. Into this microcomputer is inputted the following signals: the operation signals outputted from the display and operation portion 6, the room temperature detected by a temperature sensor 8, and the refrigerant condensation temperature detected by another temperature sensor 9. On the basis of these signals, the microcomputer of the control device 5 controls the operations of the loads 7, including the four-way valve for changing over the direction of the refrigerant in the heat pump system and the motor for the fan for delivering warmed or cooled air to the conditioned room, according to a predetermined program; at the same time, it outputs a frequency setting signal to the inverter 3 and lets the display device (consisting of light-emitting diodes) of the display and operation portion 6 display the state of operation of the compressor 4.
The display and operation portion 6 comprises, as shown in FIG. 2, a bar display 11 which displays the rotational speed or rpm of the compressor 4 as the performance level, a temperature setting device 12 which sets a target room temperature, a switch 13 for changing over the power of the indoor fan (not shown), an operation stop switch 14 for stopping the operation of the air conditioner, mode selecting switches 15 and 16 for selecting the cooling or the heating operation mode of the air conditioner, and a display device consisting of light-emitting diodes 17 and 18 which displays the operation mode, i.e., the cooling or the heating operation mode, of the air conditioner.
As mentioned above, the control device 5 consists mainly of a microcomputer, which controls the output frequency of the inverter 3 on the basis of the difference between the target temperature set by the temperature setting device 12 and the room temperature detected by the temperature sensor 8. This control of the output frequency of the inverter 3 by the microcomputer of the control device 5 is effected as follows:
The possible variation range of the temperature difference: Ta-T.sub.1 between the room temperature Ta and the target temperature T.sub.1 is divided into six zones A through F (as described hereinafter), and the output frequency of the inverter 3 is set at the levels indicated at the right-hand column of the following table at the line corresponding to zones A through F in the right hand column:
______________________________________ Ta - T.sub.1 output frequency (Hz.) ______________________________________ zone A 75 zone B 65 zone C 55 zone D 45 zone E 35 zone F stopped ______________________________________
Namely, when the temperature difference is in zone A, the inverter 3 is set at the output frequency of 75 Hz.; when in zone B, at 65 Hz., and so on; when the temperature difference is in zone F, the output of the inverter 3 is reduced to zero so that the compressor 4 is stopped.
The standard of division into these zones A through F of the temperature difference: Ta-T.sub.1 varies according as the room temperature is rising or falling. The division into zones A through F of the temperature difference: Ta-T.sub.1 in the cases of rising and falling room temperature in the cooling operation of the air conditioner is made as follows:
When the room temperature is falling, as in region X of the temperature variation curve: Ta-T.sub.1 in FIG. 3, the possible variation range of the temperature difference: Ta-T.sub.1 is divided into six zones A through F as shown at the left in FIG. 3: the temperature difference: Ta-T.sub.1 lies in zone A when it is equal to or greater than one degree centigrade; in zone B, when it is from 0.5 to one degree; in zone C when it is from 0 to 0.5 degrees; in zone D when the room temperature Ta is lower than the target temperature T.sub.1 by 0 to 0.5 degrees; in zone E when the room temperature is lower than the target temperature by 0.5 to one degree; and in zone F when the room temperature is lower than the target temperature by one degree or more.
On the other hand, when the room temperature is on the rise, as in region Y of the temperature variation curve: Ta-T.sub.1 shown in FIG. 3, the possible variation range of the temperature difference: Ta-T.sub.1 is devided into six zones A through F as shown at the right in FIG. 3: the temperature difference lies in zone A when it is equal to or greater than 1.5 degrees centigrade; in zone B, when it is from one to 1.5 degrees; in zone C when it is from 0.5 to one degree; in zone D when it is from 0 to 0.5 degrees; in zone E when the room temperature Ta is lower than the target temperature T.sub.1 by 0 to 0.5 degrees; and in zone F when the room temperature is lower than the target temperature by 0.5 degrees or more. By the way, zone D is the target zone to which the the temperature difference: Ta-T.sub.1 is controlled.
FIG. 4 shows a typical variation curve (a) of the room Ta-T.sub.1 is controlled.
FIG. 4 shows a typical variation curve (a) of the room temperature (or more precisely, the temperature difference: Ta-T.sub.1) and a curve (b) of the output frequency of the inverter 3 corresponding thereto, which are obtained when the air conditioner is controlled according to the above described method in the cooling operation mode. As shown in the figure, before the time point t.sub.1, the falling room temperature Ta is more than one degree higher than the target temperature T.sub.1, and thus the temperature difference, Ta-T.sub.1, lies in zone A, and the output frequency of inverter 3 is 75 Hz.; the room temperature therefore falls rapidly. Between time points t.sub.1 and t.sub.2, the temperature difference: Ta-T.sub.1 lies in zone B, and hence the output frequency of inverter 3 is 65 Hz., while between time points t.sub.2 and t.sub.3, the temperature difference lies in zone C, and hence the output frequency of inverter 3 is 55 Hz.; thus, the room temperature continues to fall. After the time point t.sub.3, the temperature difference, Ta-T.sub.1, comes into zone D, and the output frequency of inverter 3 is 45 Hz. Even when, thereafter, the room temperature Ta rises above the target temperature T.sub.1, the temperature difference, Ta-T.sub.1, remains in zone D, since the temperature difference is in the range of from 0 to one degree; thus, the output frequency of inverter 3 is kept at 45 Hz. This stability of the output frequency of the inverter 3 is due to the fact that the zones A through F of the temperature difference, Ta-T.sub.1, are set 0.5 degrees higher in the region where the room temperature is rising than in the region where it is falling, as described above. This gap of 0.5 degrees in the zone settings between the cases of rising and falling room temperature functions as a kind of hysteresis in the control of the room temperature. Thus, after the room temperature reaches the target level, the output frequency of the inverter 3 ceases to vary frequently, and a stable control operation is effected.
The conventional air conditioner as described above has the following disadvantage. Namely, the temperature distribution in the air-conditioned room can not be detected accurately by a single temperature sensor; as a result, even if the room temperature detected by the sensor is controlled to the target temperature, the temperature environment in the room may be deviated from the optimum condition. Since the air warmed or cooled by the air conditioner is sent out from an indoor unit of a small dimension in the case of such air conditioners, there tends to develop an unevenness in the distribution of temperature in the room. Further, the temperature distribution in the room depends on the gap between the indoor and outdoor temperatures and the heat insulating property of the room, which makes it more difficult to grasp the temperature distribution by a single sensor.